1. Field of the Invention
The present invention relates to a dechuck control method and a plasma processing apparatus.
2. Description of the Related Art
A plasma process is often performed in vacuum by evacuating gas from a processing chamber. In such a process, a processing object is placed on an electrostatic chuck (ESC) that is arranged on a stage of the processing chamber.
The electrostatic chuck includes a conductive sheet-type chuck electrode that is arranged between dielectric members. When performing a plasma process, a voltage from a direct current voltage source is applied to the electrostatic source so that the processing object is chucked to the electrostatic chuck by a Coulomb force generated from the voltage application. After the plasma process is completed, the voltage applied to the electrostatic chuck is turned off so that the processing object may be dechucked from the electrostatic chuck. To dechuck the processing object, a discharge process is performed, which involves introducing inert gas into the processing chamber to maintain the pressure within the processing chamber at a predetermined pressure level, applying a voltage of the opposite polarity with respect to the voltage applied to the electrostatic chuck during the plasma process, and then turning off the voltage application so that the electric charges of the electrostatic chuck and the processing object may be discharged. Then, support pins are raised so that the processing object may be lifted and dechucked from the electrostatic chuck.
However, the surface of the electrostatic chuck may change over time. For example, foreign substances such as reactive products generated during the plasma process may gradually build up on the surface of the electrostatic chuck to form an insulating film. In such a case, an electric charge may accumulate in the insulating film so that even when the voltage applied to the electrostatic chuck is turned off, a residual electrical charge may remain on the surface of the electrostatic chuck. Such a residual electric charge cannot be discharged by the above discharge process. As a result, the support pins may be raised while an electrostatic suction force created by the residual electric charge still remains on the surface of the electrostatic chuck so that the processing object may crack or be displaced, for example.
In this regard, Patent Document 1 discloses a system for releasing a wafer from an electrostatic chuck that involves suspending operations of the support pins for raising the wafer in order to supply to the wafer via the support pins an electric charge of an opposite polarity with respect to the electric charge generated at the rear face of the wafer rear face, and continuing to supply the electric charge from the support pins until the residual electric charge at the rear face of the wafer falls below a predetermined value. In this way, the electric charge remaining at the rear face of the wafer may be discharged.